Attempts have been made to overcome problems such as decreased sensitivity and the generation of degradation products of acidic molecules among bio-related molecules in mass spectrometry (MS). In particular, methods of esterification and amidation to inhibit the removal of sialic acid from sialic acid-containing oligosaccharide chains have been reported. For example, Japanese Unexamined Patent Publication (KOKAI) No. 2005-148054 (Patent Reference 1) describes a method for the label amidation of bio-related molecules. However, no method exists for simply, highly efficiently, and rapidly modifying acidic groups in bio-related molecules on a solid phase surface.    Patent Reference 1: Japanese Unexamined Patent Publication (KOKAI) No. 2005-148054